Linear polymers of carbon monoxide with one or more olefinically unsaturated compounds are made up of polymer units from carbon monoxide on one hand and units from the olefinically unsaturated compounds on the other hand which occur in a substantially alternating arrangement. These polymers can be prepared by contacting the monomers at elevated temperature and pressure with a catalyst composition containing a Group VIII metal and a tri(hydrocarbyl)phosphine such as tri(n-butyl)phosphine or triphenylphosphine.
A drawback of the above-mentioned catalyst compositions is their low polymerization activity. In the past the applicant has carried out an investigation in order to find out whether the polymerization activities of these catalyst compositions could be increased by modification of their phosphine component. As to the catalyst compositions containing triphenylphosphine as a phosphine component, it was found that the polymerization activity could be considerably increased by incorporating a substituent in the phenyl groups at the ortho position relative to the phosphorus atom. For example, in the copolymerization of carbon monoxide with ethene using a catalyst composition containing palladium as Group VIII metal and triphenylphosphine as a phosphine, an increase in the polymerization activity by a factor of 10 was observed when the triphenylphosphine was replaced by tris(2-methylphenyl)phosphine. A considerable increase in the polymerization activity could also be obtained by replacing the triphenylphosphine in the catalyst composition by tris(2-methoxyphenyl)phosphine. It was additionally found that an increase in the polymerization activity of the catalyst compositions containing a Group VIII metal and a tri(hydrocarbyl)phosphine could also be obtained by replacing one of the hydrocarbyl groups in the tri(hydrocarbyl)phosphine with a nitrogen-containing group wherein the nitrogen atom is connected to the phosphorus atom via a divalent organic bridging group containing at least two carbon atoms in the bridge. A considerable increase in the polymerization activity in the copolymerization of carbon monoxide with ethene could also be achieved by replacing triphenylphosphine in a catalyst composition containing palladium as a Group VIII metal with a phosphine such as 2-cyanoethyldiphenylphosphine or with a 3-(diphenylphosphino)-N,N-dimethylpropionamide.
After continued research in this subject area, it has now been found that the polymerization activity of catalysts containing a Group VIII metal and a phosphine of the general formula R.sub.1 R.sub.2 R.sub.3 P in which R.sub.1 to R.sub.3 represent identical or different optionally polar substituted hydrocarbon groups can be improved considerably more than was found possible with the aid of the previously mentioned modifications by replacing one of the groups R.sub.1 to R.sub.3 with a phosphorus-containing group in which phosphorus occurs in a 9-phosphabicyclononane structure where the smallest phosphorus-containing ring contains at least five atoms, and the bridging group incidentally has a structure such that, in the obtained diphosphorus compound, the two phosphorus atoms are connected to each other via a divalent organic bridging group containing at least two carbon atoms in the bridge. The diphosphorus compounds now proposed as catalyst component can be represented by the general formula (R.sub.1)(R.sub.2)P-R-X in which R.sub.1 and R.sub.2 represent identical or different optionally polar substituted hydrocarbon groups, and R is a divalent organic bridging group containing at least two carbon atoms in the bridge connecting the two phosphorus atoms in the diphosphorus compound to each other and, X is a 9-phosphabicyclononyl group in which the smallest phosphorus-containing ring contains at least five atoms, and the bridging group is connected via the phosphorus atom to a carbon atom of the bridging group R. It was found during the investigation that diphosphorus compounds in which two 9-phosphabicyclononyl groups occur, the phosphorus atoms of which are connected to each other via a bridging group R, are also very suitable for being used together with a Group VIII metal as catalysts in the preparation of polymers of carbon monoxide with one or more olefinically unsaturated compounds. The latter diphosphorus compounds can be represented by the general formula X-R-X.